The present invention is directed to a semiconductor component comprising a planar pn junction
Such a component can be derived, for example, from European Patent Application No. EP-A-0 176 778. When a sufficiently high voltage, referred to as the breakdown voltage, is supplied via the electrodes and inhibiting the pn junction a local breakdown of the pn junction ensues. This causes a thermal overload and, thus, a destruction of the semiconductor component very frequently occurs. The local breakdown in this known component proceeds approximately in the area where a part of the pn junction, extending parallel to a boundary surface of the semiconductor member, merges into the part of the pn junction that gradually approachs the boundary surface.
The local breakdown of the pn junction is also of great significance in power thyristors. Power thyristors are composed of a semiconductor member having four semiconductor layers of alternating conductivity types adjacent to one another. The four semiconductor layers are: an n-emitter; a p-base; an n-base; and a p-emitter. When the voltage, that is applied between a terminal at the cathode side and a terminal at the anode side that blocks the thyristor, is elevated to the value of the breakdown voltage, then a local breakdown of the pn junction proceeds that separates the p-base from the n-base and proceeds roughly parallel to a boundary surface of the semiconductor member. In general, the breakdown occurs at that edge of this pn junction lying in a lateral surface of the thyristor.
In order to avoid such an uncontrollable, local breakdown, that frequently leads to the destruction of the thyristor, European Patent Application No. EP-A-0 088 967 discloses the irradiation, with a laser beam, of the pn junction between the p-base and n-base under the central ignition electrode of the thyristor. This provides it with a bellying that diminshes the thickness of the n-base layer and initiates a controllable breakdown at a reduced breakdown voltage that occurs in the region of the bellying. This controllable breakdown leads to a precipitous ignition of the thyristor whereat a thermal destruction does not occur because of the use of a reduced breakdown voltage. The method, however, suffers the disadvantage that the reduced breakdown voltage can not be set at a defined voltage value with sufficiently desired precision and reproducibility.